1. Field of the Invention
The present invention relates to structures of a field effect type Josephson transistor and a method for manufacturing the same.
2. Prior Art
Hitherto, a diode based on a Josephson effect has been known but a transistor based on the same is not known.
A field effect type Josephson transistor has heretofore been proposed, a sectional view of which is illustrated in FIG. 10 where (91) is Si, (92) is SiO.sub.2, (93) is a source electrode, (94) is a drain electrode, (95) is a gate electrode and (96) is a tunnel gap. Specifically, SiO.sub.2 layer (92) is formed on Si substrate (91), gate electrode (95) is made of Nb or the like in a recess formed on the back surface of Si substrate (91) with the SiO.sub.2 layer (92) serving as a dielectric film, and source electrode (93) and drain electrode (94) are made of Nb or the like above gate electrode (95) so as to form tunnel gap (96) of several 10 .ANG. in width therebetween.
However, the prior art technique has a problem in that formation of such tunnel gap of several 10 .ANG. by photolithography and etching technology is extremely difficult.
In addition, it has another problem that formation of integrated circuits containing such devices is difficult.
Further, the prior art has still another problem in that accurate control of the tunnel current by the gate field is difficult since the tunnel gap is formed on the surface of the SiO.sub.2 or the like dielectric film to cause formation of a surface leakage current on the surface of the dielectric film, and the thus formed leakage current would be combined with the tunnel current.